2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Tommy Cookers.

You write:
silly old Laverda !
making and selling about 2000 3C machines with solid-mounted flat crank 1000cc and 1200cc engines

using terminology like 'feelings' and 'sense of a turbine' - that's what's not reasonable



OK.

So let’s maths and physics “talk”:



The above plots were created with the pattakon balance program.

At left of each plot it writes what it is.

The plots cover 360 crank degrees horizontally.
Spot on the units per horizontal line (say, 20Kp/horizontal line).

The plots are for the conventional I3 (crankpins 120 crank degrees from each other), unless it is written at the head of the plot that it is for the I3_Flat_Crank engine (Laverda etc).

The first plot (that like "noise") shows the free inertia force of the conventional I3. Nearly zero.

The second plot (or slide) shows the free inertia torque of the conventional I3 and its Fourier Analysis : the free inertia torque is 35Kpm (= 350mN) and is of third order (count the peaks of the curve into 360 degrees).

The third plot shows the free inertia moment of the conventional I3 (case without balance webs on the crankshaft). The peak of the inertia moment is over 250Kp*m (2,500mN).

The fourth plot shows the free inertia moment in case balance webs are secured to the crankshaft. Now the peak is about half (160Kp*m (1,600mN)) but the inertia moment is not, any longer, on the plane defined by the cylinder axes; it is a rotating inertia moment.

The fifth plot is the free inertia moment of the conventional I3 in case an external balance shaft (rotating with crankshaft speed, at opposite direction) is added. Now the peak of the free inertia moment is only 60Kp*m, is on the plane of the cylinder axes and is of second order.

The sixth plot is the free inertia force of the I3-Flat_Crank (Laverda like), with balance webs on the crankshaft. Its peak is 1,800Kp (18,000N). Compare it to the zero free inertia force of the conventional I3.

The seventh plot is the Fourier analysis (and re-synthesis) of the sixth curve. Here you can see how strong is the first order free inertia force, the second order free inertia force and so on. The first order is not as strong as the second order, however the first order has half frequency and may be more annoying.

The eight curve is the free inertia torque of the I3-Flat_Crank. It is mainly of second order and its peak is 95Kp*m, about three times higher than the free inertia torque of the conventional I3.
In this curve you have to add the combustion torque curve, which is quite asymmetrical curve with a big pulse between 0 and 180 degrees, and a small (half in size) pulse from180 to 360 degrees.

The last curve is the free inertia moment of the I3_Flat_Crank. Net zero due to the symmetry of the engine (the two side pistons at zero phase difference).


Having said all these, these two engine have several reasons to be quite different as regards their vibrations. Don’t they?


For the combustions, the one has a strong pulse per 360 degrees and a weak pulse in the middle of the 360 degrees intervals. It would remind a single cylinder. If you add the strong 2nd order free inertia torque. . .
The other has equal, equally distributed power pulses (one per 120 crank degrees), which – combined with the weak symmetrical 3rd order inertia torque has all it needs to remind turbine.


Now it is your turn to explain what makes the vibrations of the two arrangements (Laverda’s and conventional) similar.


PS1.

The engines (conventional I3 and I3_flat_crank) have same pistons, same connecting rods, same cylinder axes distance)


PS2.

It is a pity that the “engineers” / “scientists” of the forum can’t get how a personal flying device can recover from nose-down flight to nose up flight with only control the body of the pilot.
Maybe the specific problem of control is too simple for them to deal with.

Thanks
Manolis Pattakos

[nzjrs]

PS2.

It is a pity that the “engineers” / “scientists” of the forum can’t get how a personal flying device can recover from nose-down flight to nose up flight with only control the body of the pilot.
Maybe the specific problem of control is too simple for them to deal with.

Manolis, this is not very polite. To be polite doesn't cost anything as you said.

Are you still preparing the measurements and photos I suggested in my post?

P.S. Your specific objection is you once again not understanding the pissing off the side of a cruise ship and controllability example. Please consider the analogy "open minded"; and if you still cannot get it, let me know what exactly you can't get.

[uniflow]

manolis, HP on my OP boat engine?
Didn't have a dyno back then but I did look up the power required for a single stage Colorado unit, standard pitch prop. Accounting for the gear reduction ( engine 9500 ) , the engine was producing approx 60 HP, 440cc.
Not bad for a first off of design, no tuned pipes, but Im sure we can do a lot better with this next design. We never kept fuel burn records but needless to say we were not filling it up all the time like an outboard twostroke.

[NathanE]

PS2.

It is a pity that the “engineers” / “scientists” of the forum can’t get how a personal flying device can recover from nose-down flight to nose up flight with only control the body of the pilot.
Maybe the specific problem of control is too simple for them to deal with.

Thanks
Manolis Pattakos

It's probably simple if you look like this



Sadly to much beer and too many pies make this unlikely for me

[manolis]

Hello Uniflow

You write:
“manolis, HP on my OP boat engine?
Didn't have a dyno back then but I did look up the power required for a single stage Colorado unit, standard pitch prop. Accounting for the gear reduction ( engine 9500 ) , the engine was producing approx 60 HP, 440cc.
Not bad for a first off of design, no tuned pipes, but Im sure we can do a lot better with this next design. We never kept fuel burn records but needless to say we were not filling it up all the time like an outboard twostroke”


So 60HP at 9.5Krpm from 440cc

For a prototype it is great. Good for you.

However, is it really high for a two-stroke revving so high?

Let’s calculate its torque at the peak power:

60 / (1.4*9.5) = 4.5Kp*m (or 45mN).

Together with its 440cc capacity, it translates to ~100mN per liter of displacement.

For a good 4-stroke it is good, not great (the Ducati Panigale V-2 makes about 110mN per lit of displacement).

But for a 2-stroke? (even without tuned exhaust).


Here is a dyno of a KTM EXC: 300cc (tpi?, substantially lower revs, 57 HP).




I really respect your work (as I respect the work of all the tinkers and thinkers around the world).

What I can't get is your persistence with reliability and performance.
You can't compete an engine manufacturer in these areas because he has better materials, he has better machinery, he has better tools, his staff makes only this (engines) and has long experience in this, he has also lots of money to spend.

So, when you see an engine like the all-cast OPRE Tilting "revving to the sky", and knowing that it is the first try of someone who never before made cast parts, don't ask how many hours it will last.
To work so high and so smoothly is an achievement by itself.
When the basic principles are correct, the rest (reliability, performance) will come with reasonable improvements (better materials, better thermal treatment, better manufacturing accuracy etc).

Thanks
Manolis Pattakos

[uniflow]

manolis, you are right, when I see your engine reving in the sky, I will be amazed although I will stand well clear .
You do understand my boat engine is a one off, design and build? Opposed Piston. Never before been such a layout, I want to see your engine do the same, then I see it as successful, thats my threshold.

[henry]

@manolis

How do you plan to measure the performance of your power unit? Will you find a dyno and measure power, or perhaps attach props and measure thrust? I would think the latter might be easier since you could mount it as designed for the application. This would allow you to verify other things, such as cooling, since you would have the prop wash. Given your design I would think the only significant forces on such a structure would come from the thrust it could be fairly simple.

You might even trunnion mount it In a suitable structure and verify some of your thoughts on controllability.

[coaster]

I've seen gokart tuners use a hydraulic vane pump, a tap load and pressure gauge.
A bit of math and im sure you could get within 5 percent, maybe better.

[coaster]

Double post, wierd.

[manolis]

Hello Henry.

You write:
“How do you plan to measure the performance of your power unit? Will you find a dyno and measure power, or perhaps attach props and measure thrust? I would think the latter might be easier since you could mount it as designed for the application. This would allow you to verify other things, such as cooling, since you would have the prop wash.”


To attach the propellers and measure the thrust is the most direct way because what really matters in the Portable Flyer is not the power output of the engines, but the thrust from the propellers.

As you mention, the propellers provide high speed air for the cooling of the engines, allowing the operation / test for hours with the Portable Flyer secured to a basis on the ground.



You also write:
“Given your design I would think the only significant forces on such a structure would come from the thrust it could be fairly simple.”


Exactly.
Here is how the https://www.pattakon.com/pattakonFly.htm web page starts):

• Two counter rotating crankshafts share the same combustion chamber keeping the basis perfectly rid of inertia vibrations and of combustion vibrations.
  
  The basis (i.e. the rider / pilot) needs not to provide any reaction torque (not even at extreme changes of revs and load).
  
  With the symmetric counter-rotating propellers (and crankshafts), the total "gyroscopic rigidity" is zero, i.e. the rider can "instantly" (as instantly as with the propellers stopped) vector the thrust to the desirable direction.
  
  The above make "a true neutral propulsion unit": neither vibrations, nor reaction torque, nor gyroscopic rigidity; only a force that can "instantly" and effortlessly be vectored towards the desirable direction.

You also write:
“You might even trunnion mount it In a suitable structure and verify some of your thoughts on controllability.”


The simplest way is, after the measurement of the “static” thrust (and the reliability tests) to secure a saddle (the brown part) on pilot’s back / torso, then secure the Portable Flyer on the saddle and make tethered tests (at, say, no more than half a meter / 2ft from the ground) .



I suppose it will be fun to jump or run (not tethered, any longer) wearing it and keeping “half-throttle”, i.e. with the Portable Flyer taking only a part (say, the 80%) of the total weight.

Thanks
Manolis Pattakos

[Rodak]

It is a pity that the “engineers” / “scientists” of the forum can’t get how a personal flying device can recover from nose-down flight to nose up flight with only control the body of the pilot.

Really manolis, when you post something like 'engineers' in quotes you are saying that they are not engineers but fakes or dullards or idiots. You mentioned one should not say 'shut up' to you; don't say 'engineer' in a demeaning manner to me. In the United States the term 'engineer' has a different meaning from England; in the U.S. of A. to use the title 'engineer' requires a degree. To use the term 'professional engineer' requires certification through testing and carries legal responsibilities; so 'engineer' here means a university degreed professional, not a mechanic. You have no idea who I am or what I have done. I have been involved in composite design for the C-17, the B-2 bomber, marine off shore applications including off shore oil rigs, mooring equipment, tug boat equipment, etc. I am an experience CAD designer and have worked in other fields. Your intransigence at accepting that others might see design flaws with your 'control systems' for your flier is what keeps most of us posting here. You are making some fundamental mistakes with control and when help is offered you don't respond with information that might clarify the situation. Good luck.

Maybe the specific problem of control is too simple for them to deal with.

I suspect not.

[manolis]

Hello Rodak.

you write:
”What I don't agree is that it is controllable by moving legs and arms while strapped into a rigid frame.
. . .
I'm curious, if the flyer becomes inverted how does the pilot pull out before augering in?”


Let’s simplify the problem.

Think of an astronaut wearing two small rockets rigidly secured on the left and right sides of torso / back.

Suppose that when the astronaut is at straight posture the thrust from the two rockets is parallel to astronaut’s spine.

Suppose the astronaut is 500m above the ground of the moon and is falling head-down, with the rockets pushing straight downwards. Astronaut’s body is at straight posture. The thrust passes from the center of gravity.

If astronaut’s body stays at the straight posture, the accelerating fall will continue till hitting the ground.

But the astronaut can easily change from “straight” head-down to fetal posture:



displacing the centrer of gravity away from the thrust (to the right in the photo).

Now the thrust force F is eccentric from the centrer of gravity.
According physics, the thrust force F is equivalent to an equal and parallel force F’ passing from the center of gravity, plus a torque T equal to the thrust force F times its eccentricity X from the center of gravity.

Equivalent means that the result is absolutely the same either you keep the F force, or you replace it by the force F’ and the torque T.

While the force F’ continues to accelerate the astronaut towards the ground, the torque T turns the astronaut (together with the rockets secured on astronaut’s body) about the center of gravity (COUNTER-clockwise in the photo).

I.e. the torque T turns the thrust direction.

When the astronaut has turned for 180 degrees:



the thrust is vectoring upwards decelerating the fall and then accelerating the astronaut upwards.

The astronaut has to restore to straight posture to cancel out the torque T and prevent further turning.


Is there any objection to the previous?

Thanks
Manolis Pattakos

[Rodak]

Why not answer my previous post? Your description is simply a word salad with pretty pictures (inverted). Show some data about the influence of legs and arms in the air stream and their aerodynamic input; it would be easy to make models and actually test things. I can write all sorts of stories about how things work and they would be beautiful; the real test is to provide data.

This is just a re-post of your previous response. Repetition may be the mother of learning, but not in this case.

[manolis]

Hello all.

Can an English speaking member of this forum translate to Rodak my last post?



EDIT:

I really have to thank Rodak for his question:

• "I'm curious, if the flyer becomes inverted how does the pilot pull out before augering in?”

It is the worst schenario: what if at some moment the pilot (or astronaut in order to avoid the air lift and drag) is going "nose down" straight to the ground?

If the pilot (or astronaut) can recover from such a situation, everything else is "piece of cake".

I am still waiting for one justified "objection", from anybody.

If you get how the astronaut recovers from a "head down" condition, then the understanding of the control over the Portable Flyer is simple and easy.

Thanks
Manolis Pattakos

[nzjrs]

I am still waiting for one justified "objection", from anybody.

If you have a lot of free waiting time you could take some of the photos and measurements I suggested in my post. That way we could do a bit of non photographic modeling.